Nodes

Your P2P node is a class where you can add message handlers for your protocol. Every technique for making P2P TCP connections in P2PD ultimately passes messages back to these handlers. Where P2PD really shines is it’s the only P2P networking framework that’s designed to run across multiple network interfaces and address families (IPv4 and IPv6.)

The reason this is important is different network interfaces often have completely different qualities in terms of being able to reach services behind them. So a design that works for multiple interfaces maximizes peer-to-peer reachability. A direct example of this is that of mobile phones where one interface might be for mobile data and another for Wi-Fi.

from p2pd import *

# Put your custom protocol code here.
async def msg_cb(msg, client_tup, pipe):
    # E.G. add a ping feature to your protocol.
    if b"PING" in msg:
        await pipe.send(b"PONG", client_tup)

async def example():
    # Start a new P2P node with your protocol.
    node = await P2PNode()
    node.add_msg_cb(msg_cb)

When the node starts it may take a few seconds to load everything. This is because external addresses for each interface have to be loaded via STUN; MQTT server connections opened; clock skew calculated with NTP; and any ports forwarded or pin holed. You can configure whether you want to try use UPnP to improve reachability for your node.

UPnP will need to be enabled on the router used for one of your nodes interfaces. But in practice many people aren’t going to have this setup or may not want to enable it for security reasons. Fortunately, reachability in P2PD does not depend solely on UPnP support.

from p2pd import *

node_conf = dict_child({
    # Port forwarding (IPv4) and pin holes (IPv6)
    "enable_upnp": True,

    # MQTT server no -- need at least 1 for P2P connections.
    "sig_pipe_no": SIGNAL_PIPE_NO,
}, NET_CONF)

async def example():
    if_names = await list_interfaces()
    ifs = await load_interfaces(if_names)
    node = await P2PNode(ifs=ifs, port=1337, conf=node_conf)
    await node.close()

P2PD has a data directory in your home folder. This folder stores private keys for node nicknames and for encrypting P2P signaling messages. The folder also stores mutexes to prevent zombie daemons from taking the same listen ports in P2PD (this is useful when combined with socket options that allow servers to be instantly restarted.)

The most interesting stuff is yet to come.